One-step hologram (including holographic stereogram) production technology has been used to satisfactorily record holograms in holographic recording materials without the traditional step of creating preliminary holograms. Both computer image holograms and non-computer image holograms may be produced by such one-step technology. In some one-step systems, computer processed images of objects or computer models of objects allow the respective system to build a hologram from a number of contiguous, small, elemental pieces known as elemental holograms or hogels. To record each hogel on holographic recording material, an object beam is passed through the rendered image (e.g., as displayed on a spatial light modulator (SLM)) and used with a reference beam to create an interference pattern on the holographic recording material. Examples of techniques for one-step hologram production can be found in the U.S. Patent Application entitled xe2x80x9cMethod and Apparatus for Recording One-Step, Full-Color, Full-Parallax, Holographic Stereograms,xe2x80x9d Ser. No. 09/098,581 (hereafter xe2x80x9cthe ""581 applicationxe2x80x9d), naming Michael A. Klug, Mark E. Holzbach, and Alejandro J. Ferdman as inventors, and filed on Jun. 17, 1998, which is hereby incorporated by reference herein in its entirety.
There is great interest in holograms with very wide viewing angles of 180xc2x0-360xc2x0. In many cases, xe2x80x9cwrappingxe2x80x9d the hologram image on a curved substrate during the hologram recording produces images with a broad angle of view when the images are mounted on the curved substrate. Such holograms enable viewing by a much larger audience than standard flat-format holograms. Additionally, curved format holograms can potentially improve the illusion of a suspended image, since the image is no longer anchored to a planar surface. In some cases, the image can be made to appear at the radial center of the mounting substrate, either as a virtual (behind the hologram plane) or aerial (in front of the hologram plane) image.
The difficulty in mounting, recording and illuminating curved-format holograms, however, has limited the usefulness and practice of this technique. It is particularly difficult to record holograms on substrates curved in two dimensions, since such holograms require the holographic recording material (e.g., photopolymerizable compositions, dichromated gelatin, and silver halide emulsions) to be directly coated onto such a substrate. Cylindrically-curved substrates are generally easier to accommodate, since they are curved in only one dimension and can be flattened temporarily, thereby simplifying recording and film processing.
There is wide and varied prior art for cylindrical-format holograms, beginning with the xe2x80x9cMultiplexxe2x80x9d hologram developed by Lloyd Cross in the early 1970""s, proceeding most recently to Benton""s xe2x80x9cAlcovexe2x80x9d hologram of t he late 1980""s. U.S. Pat. No. 4,4834,476, entitled xe2x80x9cReal Image Holographic Stereograms,xe2x80x9d and naming Stephen A. Benton as inventor, which is hereby incorporated by reference herein in its entirety, discloses a hemi-cylindrical format holographic stereogram (the xe2x80x9calcove hologramxe2x80x9d) comprised of 900 slit holograms that are 1 millimeter wide by 300 millimeters high. An example of a reflection alcove hologram 100 is shown in FIG. 1A. The image volume can occupy any portion of the solid angle subtended by the intersection of the viewer""s eyes and the hemi-cylinder 102. The image(s) 104 incorporated in the reflection alcove hologram 100 are typically computer-generated and processed graphics, and the hologram itself can be reconstructed with a standard white light source 106 placed above and centered relative to the hemi-cylinder 102.
Although the reflection alcove hologram can produce imagery with a wide (up to 180xc2x0) viewing angle, a number of limitations are notable. Referring to FIGS. 1B and 1C, which show side and top views, respectively, of reflection alcove hologram 100, the reference illumination angle from light source 108 for the reflection alcove hologram 100 is fixed by the recording geometry, e.g., the angle of incidence of the reference beam with respect to the holographic recording material. Reflection alcove hologram 100 is horizontal parallax-only, and each of the component strip holograms has a horizontal viewing angle of about 53xc2x0, as shown in FIG. 1C. So, for example, a projected image about 275 mm across can be seen over an angle of approximately 90xc2x0-100xc2x0 before cut off of the edges of the image is noticeable. Reflection alcove hologram 100 displays parallax in only the horizontal direction, and there is no apparent change in the position of an object with variations in the vertical viewpoint. Moreover, the same vertical image information is distributed across the entire 30xc2x0 viewing angle (e.g., vertical viewing zones) for each of the hologram points 110, 120, and 130. Thus, viewability and image information are severely limited by the recording geometry and techniques.
The reflection alcove display is also particularly sensitive to defects in the mounting substrate. The lack of vertical parallax between the image and the hologram surface places the image vertical focus at the hologram surface, and this impression is heightened by any cosmetic defects in the hologram or its substrate.
Additionally, Benton describes the possibility of producing multi-color imagery in the reflection alcove as a process requiring exposure in a single wavelength with tedious multiple emulsion swelling steps between, and carefully calibrated image processing for each step. This is due primarily to the existence of optical elements in the recording system that only function properly with the monochromatic laser light, including holographic optical elements (HOEs) and non-achromatic refractive optics.
The use of specialized HOEs and cylindrical optics also make it difficult to scale the reflection alcove hologram, since doing so would likely involve incorporating optics with at least one dimension measuring the same size as the hologram itself. Thus, cylinder heights much larger than 300 millimeters would be very difficult to demonstrate in a nearly seamless fashion. Finally, the horizontal parallax-only characteristic of the reflection alcove necessitates a significant amount of astigmatism in the imaging system, thus limiting the maximum depth tolerable for comfortable viewing.
Given these, and other limitations of the prior art, it is therefore desirable to provide wide field of view, full-parallax, full-color holograms that are adaptable to substrates that are curved in one, two, or three dimensions, including cylindrical, conical, and spherical surfaces. It is also desirable to provide holograms on curved substrates that are scalable to unlimited size.
The current invention comprises the recording of full parallax, one-step, full color holographic stereograms that can be mounted on a curved substrate after recording. It also comprises mounting the hologram on a substrate that is curved in on a substrate that can be curved in one or two dimensions, thereby producing any arbitrary shape. The hologram is comprised of one or more tiles, and thus curved holograms of unlimited size can be generated. The hologram is adaptable to a variety of curved substrates including hemi-cylindrical substrates with opaque backing to allow up to 180xc2x0 of horizontal view zone, and full cylinders with transparent backing to allow viewing through 360xc2x0 horizontally.
In one embodiment, the present invention is a system for generating a holographic display on a curved substrate. The holographic display includes an image recorded on one or more tiles, and each tile is comprised of one or more holographic elements (hogels). The one or more tiles are mounted on the curved substrate. An image generation module is operable to allow a designer to specify a reference beam angle for each hogel and at least one of a radius of curvature for the substrate, a hogel orientation with respect to an image volume, a hogel orientation with respect to the substrate, and a hogel image orientation.
In another embodiment, the present invention includes a holographic display on a curved substrate comprised of a plurality of hogels recorded on the tile. The tile is mounted on the curved substrate. A plurality of hogels are recorded on the tile by varying at least one of a hogel orientation with respect to an image volume, a hogel orientation with respect to the substrate, and a hogel image orientation.
In another embodiment, a method for generating a holographic display on a curved substrate is provided that includes
specifying a radius of curvature for the substrate;
specifying an angle of illumination for each of a plurality of hogels; and
determining for each of the plurality of hogels at least one of a hogel orientation with respect to an image volume, a hogel orientation with respect to the substrate, and a hogel image orientation based on the curvature of the substrate and the angle of illumination for the respective hogel.
In each of the embodiments, the shape of the substrate can be hemi-cylindrical, cylindrical, conical, or spherical. Other, irregularly shaped surfaces can also be used. In the case of hemi-cylindrical or cylindrical surface, another cylindrical section having a radius larger than the substrate can be positioned around the substrate to provide a background for the holographic display.
The present invention has several advantages over alternative technologies. First, the present invention achieves curved, full parallax holographic displays that provide more depth cues than displays currently available in the prior art. The present invention also provides holographic displays that can be viewed from a variety of viewpoints including over and under the imaged object, while removing depth limiting and potentially distorting astigmatism. The present invention can also produce full-color imagery without the need for tedious and difficult emulsion swelling, and triple exposures. The displays are inherently scalable using tiling techniques disclosed in the ""581 application in a manner similar to that for tiled flat format holograms. The ability in the current recording system to redirect the reference beam for each hogel makes it possible to tailor the illumination angle and distance independently of the print or substrate geometry. The current invention further enables the hologram to be mounted on any curved surface, instead of being dictated by fixed printer parameters, as in the alcove case. Finally, each hogel in the current invention has over twice the viewing angle as the alcove case, enabling much larger images to be produced, and enabling visibility of the image over a much broader angle.
Those having ordinary skill in the art will readily recognize that the systems and techniques described above and in the claims can be implemented using a variety of different computer graphics rendering methods. In particular, scan-line rendering, light-field models, and ray tracing are all examples of computer graphics techniques that can be uses to implement the present invention. Moreover, both software-based and hardware-based rendering systems (or some combination of the two) can be used to implement the present invention.
The foregoing has outlined rather broadly the objects, features, and technical advantages of the present invention so that the detailed description of the invention that follows can be better understood.